Integrated spin valve head

ABSTRACT

Currently, the shield-to-shield separation of a spin valve head cannot be below about 800 Å, mainly due to sensor-to-lead shorting problems. This problem has now been overcome by inserting a high permeability, high resistivity, thin film shield on the top or bottom (or both) sides of the spin valve sensor. A permeability greater than about 500 is required together with a resistivity about 5 times greater than that of the free layer and an M r T value for the thin film shield that is 4 times greater than that of the free layer. Five embodiments of the invention are described.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic recording withparticular reference to improving linear resolution.

BACKGROUND OF THE INVENTION

The present invention is concerned with the manufacture of the readelement in a magnetic disk system. This is a thin slice of materiallocated between two magnetic shields which we will refer to a primaryshields. The principle governing operation of the read sensor is thechange of resistivity of certain materials in the presence of a magneticfield (magneto-resistance). In particular, most magnetic materialsexhibit anisotropic behavior in that they have a preferred directionalong which they are most easily magnetized (known as the easy axis).The magneto-resistance effect manifests itself as a decrease inresistivity when the material is magnetized in a direction perpendicularto the easy axis, said decrease being reduced to zero when magnetizationis along the easy axis. Thus, any magnetic field that changes thedirection of magnetization in a magneto-resistive material can bedetected as a change in resistance.

It is now known that the magneto-resistance effect can be significantlyincreased by means of a structure known as a spin valve (SV). Theresulting increase (known as Giant magneto-resistance or GMR) derivesfrom the fact that electrons in a magnetized solid are subject tosignificantly less scattering by the lattice when their ownmagnetization vectors (due to spin) are parallel (as opposed toanti-parallel) to the direction of magnetization of the solid as awhole.

The key elements of a spin valve structure are two magnetic layersseparated by a non-magnetic layer. The thickness of the non-magneticlayer is chosen so that the magnetic layers are sufficiently far apartfor exchange effects to be negligible (the layers do not influence eachother's magnetic behavior at the atomic level) but are close enough tobe within the mean free path of conduction electrons in the material.If, now, these two magnetic layers are magnetized in opposite directionsand a current is passed through them along the direction ofmagnetization, half the electrons in each layer will be subject toincreased scattering while half will be unaffected (to a firstapproximation). Furthermore, only the unaffected electrons will havemean free paths long enough for them to have a high probability ofcrossing the non magnetic layer. However, once these electron ‘switchsides’, they are immediately subject to increased scattering, therebybecoming unlikely to return to their original side, the overall resultbeing a significant increase in the resistance of the entire structure.

In order to make use of the GMR effect, the direction of magnetizationof one the layers must be permanently fixed, or pinned. Pinning isachieved by first magnetizing the layer (by depositing and/or annealingit in the presence of a magnetic field) and then permanently maintainingthe magnetization by over coating with a layer of antiferromagneticmaterial. The other layer, by contrast, is a “free layer” whosedirection of magnetization can be readily changed by an external field(such as that associated with a bit at the surface of a magnetic disk).

Structures in which the pinned layer is at the top are referred to astop spin valves. Similarly, It is also possible to form a ‘bottom spinvalve’ structure where the pinned layer is deposited first. Although notdirectly connected to the GMR effect, an important feature of spin valvestructures is a pair of longitudinal bias stripes that are permanentlymagnetized in a direction parallel to the long dimension of the device.Their purpose is to prevent the formation of multiple magnetic domainsin the free layer portion of the GMR sensor, particularly near its ends.

FIG. 1 shows a typical structure that embodies the features describedabove. As noted above, the device is sandwiched between two primaryshields 11 and 12. Currently, the shield-to-shield separation of a spinvalve head cannot be below about 800 Å, mainly due to thesensor-to-shield shorting problem. This is pointed to in the figure byarrow 13. Since improvements in the density of recorded data requirethat this distance be reduced below 800 Å, there is a need for astructure (and a process for manufacturing it) that is not susceptibleto said shorting problem.

An application that describes a structure that is related to thatdisclosed by the present invention was filed on Sep. 30, 1999 asapplication Ser. No. 09/408,492. Additionally, a routine search of theprior art was performed and the following references of interest werefound:

In U.S. Pat. No. 5,978,182, Kanai et al. show a SV with a first softmagnetic layer. In U.S. Pat. No. 5,608,593, Kim et al. shows a SV with anon-magnetic (e.g., Cr) under-layer. Takada et al show a stabilizinglayer with an under-layer of Cr and a hard magnetic layer in U.S. Pat.No. 5,828,527, while Ohsawa et al. (U.S. Pat. No. 5,777,542), Dykes etal. (U.S. Pat. No. 5,668,688), and Hsiao et al. (U.S. Pat. No.5,999,379) all show related SV devices with shield layers.

SUMMARY OF THE INVENTION

It has been an object of the present invention to provide a spin valvestructure that is free of internal electrical shorting by maintaining arelatively large shield-to-shield spacing while continuing to obtainvery narrow feedback pulse widths.

Another object of the invention has been to provide a process formanufacturing said spin valve structure.

A further object has been that said structure be given its longitudinalbias through either permanent magnet or exchange magnet means;

A still further object has been that said structure be either a top or abottom spin valve.

These objects have been achieved by inserting a high permeability, highresistivity, thin film shield on the top or bottom (or both) sides ofthe spin valve sensor. A permeability greater than about 500 is requiredtogether with a resistivity about 5 times greater than that of the freelayer and an M_(r)T value for the thin film shield that is 4 timesgreater than that of the free layer. Five embodiments of the inventionare described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows how a structure made according to earlier teachings issubject to shorting (through the dielectric layer that insulated theshield from the sensor) if made too thin.

FIGS. 2 and 3 show bottom spin valve structures with permanent magnetbiasing, having a single thin film shield, as taught by the presentinvention.

FIG. 4 shows a bottom spin valve structure with exchange magnet biasing,having a single thin film shield, as taught by the present invention.

FIG. 5 shows a top spin valve structure with exchange magnet biasing,having a single thin film shield, as taught by the present invention.

FIG. 6 shows a bottom spin valve structure with permanent magnetbiasing, having two thin film shields, as taught by the presentinvention.

FIG. 7 compares read back signal pulse shape for structures with andwithout the thin film shield.

FIG. 8 plots voltage against total magnetic moment for structures withand without the thin film shield.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As already noted above, present SV designs cannot have theirshield-to-shield spacing thicknesses reduced below about 800 Å becauseof shorting through the dielectric insulating coverage over theconductor lead. In dual stripe MR structures, it has been observed thatif one of the MR stripes is not performing correctly, the signalcontribution is dominated by the other MR, so that the read back pulsewidth, PW₅₀, is reduced. PW₅₀ is the pulse width measured at the 50% ofamplitude point (in nanoseconds or nanometers). It is measured at lowfrequency to avoid interference between adjacent pulses.

The present invention solves this problem by the insertion of a highpermeability, high resistivity thin film shield on the top or bottom (orboth) sides of the spin valve sensor. Examples of materials suitable forthe thin film shields include (but are not limited to)nickel-iron-chromium, cobalt-niobium-zirconium, andcobalt-niobium-hafnium. We now describe five embodiments of the presentinvention. Although each embodiment is described in terms of the processfor its manufacture, the structure of each embodiment will becomeapparent as each manufacturing process is disclosed. The followingcompositions and thickness ranges are common to all embodiments: TABLE ILAYER COMPOSITION THICKNESS (Å) free Co₉₀Fe₁₀, Ni₈Fe₁₉  5-50non-magnetic spacer Cu 12-22 pinned Co₉₀Fe₁₀ 10-30 pinning Ni₄₅Mn₅₅,Mn₅₀Pt₅₀  80-200 dielectric Al₂O₃, AlN 100-200 Thin film shield NiFeCr,CoZrNb,  50-400 CoHfNb, CoZrHf, CoFeX (X = Cr, N, Ta, Ti) decouplingTaO, NiCr, NiFeCr 20-50

First Embodiment

This process is for manufacturing a top spin valve structure. It beginswith the provision the first (lower) of the two primary magneticshields. This can be seen as layer 15 in FIG. 2 on which dielectriclayer 17 is deposited, followed by the deposition of free layer 21. Thisis followed by the deposition of non-magnetic layer 22 onto which isdeposited pinned layer 23. Next, onto pinned layer 23 there is depositedanti-ferromagnetic layer 24 for use as a pinning layer. This completesformation of the spin valve itself.

Now follows a key feature of the invention. On anti-ferromagnetic layer24, decoupling layer 25 is deposited, followed by the deposition of thinfilm shield 26. The purpose of the decoupling layer is to avoid anyexchange coupling of the thin film shield by layer 24. The thin filmshield is a layer of ferromagnetic material having a permeabilitygreater than about 500. It needs to have as high an electricalresistivity as possible within other constraints of the structure. It isrequired to be at least 5 times more resistive than the free layer.Since the latter is about 25 micro-ohm-cm, a value greater than about125 micro-ohm-cm is to be preferred. The thickness of the thin filmshield should be such that the moment-thickness product (of the thinfilm shield) is 2-5 times that of the free layer. The presence of thisthin film shield allows relatively thicker dielectric layers to be used,thereby reducing or eliminating the chances of shorting, while stillbeing able to obtain very narrow feedback pulse widths (namely PW₅₀).

To initiate completion of the structure, trench 29 is formed usingconventional patterning and etching. This trench extends through thinfilm shield 26 down as far as the top surface of dielectric layer 17.The trench has a sidewall 30 that slopes at an angle of about 20degrees. Onto this sidewall, as well as the exposed surface ofdielectric layer 17, is selectively deposited layer 27 of aferromagnetic material (such as CoCrPt) that is suitable for use as apermanent magnet, the direction of permanent magnetization being set bya field that is present during or after deposition of the layer. Layer27 will serve to provide longitudinal bias to the structure, asdiscussed earlier.

With layer 27 in place, a layer of conductive material 28, suitable foruse as a connecting lead to the structure, is selectively depositedthereon. This is followed by the deposition of second dielectric layer18 onto which is deposited upper primary magnetic shield 16.

Second Embodiment

This process is also for manufacturing a top spin valve structure.Referring now to FIG. 3, this embodiment begins with the provision ofthe first (lower) of the two primary magnetic shields 15 on whichdielectric layer 17 is deposited. Now follows a key feature of theinvention, namely the deposition of thin film shield 36. The thin filmshield is a layer of high permeability (greater than about 500)ferromagnetic material. It needs to have as high an electricalresistivity as possible within other constraints of the structure. It isrequired to be at least 5 times more resistive than the free layer.Since the latter is about 25 micro-ohm-cm, a value greater than about125 micro-ohm-cm is to be preferred. The thickness of the thin filmshield should be such that the moment-thickness product (of the thinfilm shield) is 2-5 times that of the free layer. The presence of thisthin film shield allows relatively thicker dielectric layers to be used,thereby reducing or eliminating the chances of shorting, while stillbeing able to obtain very narrow feedback pulse widths.

With the thin film shield in place, decoupling layer 25 is laid downfollowed by the deposition of free layer 21. This is followed by thedeposition of non-magnetic layer 22 onto which is deposited pinned layer23. Next, onto pinned layer 23 there is deposited anti-ferromagneticlayer 24 for use as a pinning layer. This completes formation of thespin valve itself.

Completion of the structure then continues with the formation of trench29, using conventional patterning and etching. This trench extendsthrough layer 24 down as far as the top surface of dielectric layer 17.The trench has a sidewall 30 that slopes at an angle of about 20degrees. Onto this sidewall, as well as the exposed surface ofdielectric layer 17, is selectively deposited layer 27 of aferromagnetic material (such as CoCrPt) that is suitable for use as apermanent magnet, the direction of permanent magnetization being set bya field that is present during deposition of the layer or by laterannealing in such a field. Layer 27 will serve to provide longitudinalbias to the structure, as discussed earlier.

With layer 27 in place, a layer of conductive material 28, suitable foruse as a connecting lead to the structure, is selectively depositedthereon. This is followed by the deposition of second dielectric layer18 onto which is deposited upper primary magnetic shield 16.

Third Embodiment

This process is also for manufacturing a top spin valve structure. Werefer now to FIG. 4 which begins with the provision of the first (lower)of the two primary magnetic shields 15 onto which is depositeddielectric layer 17. Then, on a selected area at the surface of layer17, a layer of conductive material 47, suitable for use as a connectinglead to the structure, is deposited. Then, on layer 47 only, layer 48 ofa ferromagnetic material suitable for use as an exchange magnet isdeposited. This will serve to provide the needed longitudinal bias forthe structure, as discussed above.

Then, free layer 21 is deposited over the full surface followed by thedeposition of non-magnetic layer 22 onto which is deposited pinned layer23. Next, onto pinned layer 23 there is deposited anti-ferromagneticlayer 24 for use as a pinning layer.

Now follows a key feature of the invention. On anti-ferromagnetic layer24, decoupling layer 25 is deposited, followed by the deposition of thinfilm shield 46. The purpose of the decoupling layer is to avoid anypinning of the thin film shield by layer 24. The thin film shield is alayer of high permeability (greater than about 500) ferromagneticmaterial. It needs to have as high an electrical resistivity as possiblewithin other constraints of the structure. It is required to be at least5 times more resistive than the free layer. Since the latter is about 25micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to bepreferred. The presence of this thin film shield allows a relativelylarge shield-to-shield spacing to be maintained (thereby reducing oreliminating the chances of shorting) while still being able to obtainvery narrow feedback pulse widths.

Since the lead and biasing structure is already in place, all thatremains to complete this embodiment is the deposition of seconddielectric layer 18 onto which is deposited upper primary magneticshield 16.

Fourth Embodiment

Unlike the previous three embodiments, this process is for manufacturinga bottom spin valve structure. Referring to FIG. 5, it begins, asbefore, with the provision of the first (lower) of the two primarymagnetic shields 15 onto which dielectric layer 17 is deposited. A keyfeature of the invention now follows, namely the deposition of thin filmshield 56. The thin film shield is a layer of high permeability (greaterthan 500) ferromagnetic material. It needs to have as high an electricalresistivity as possible within other constraints of the structure. It isrequired to be at least 5 times more resistive than the free layer.Since the latter is about 25 micro-ohm-cm, a value greater than about125 micro-ohm-cm is to be preferred. The thickness of the thin filmshield should be such that the moment-thickness product (of the thinfilm shield) is 2-5 times that of the free layer. The presence of thisthin film shield allows relatively thicker dielectric layers to be used,thereby reducing or eliminating the chances of shorting, while stillbeing able to obtain very narrow feedback pulse widths (namely PW₅₀).

With the thin film shield in place, decoupling layer 25 is laid downfollowed by the deposition of anti-ferromagnetic layer 24. This isfollowed by the deposition of pinned layer 23 onto which is depositednon-magnetic layer 22. Next, onto non-magnetic layer 22 there isdeposited free layer 21 which completes formation of the spin valveitself.

To initiate completion of the structure, shallow trench 59 is formedusing conventional patterning and etching. This trench extends part waythrough the free layer 21. On the part of the free layer that liesoutside the trench, capping layer 51 of tantalum, tantalum oxide, andalumina, among others, is deposited. Its purpose is to provideprotection against oxidation or other forms of contamination. On thepart of the free layer that forms the base of the trench, refill layer52 of the same material as used for the free layer (typicallypermalloy).

Layer 48, comprising a ferromagnetic material suitable for use as anexchange magnet is then selectively deposited onto the trench baseportion of layer 21 where it will provide longitudinal bias to thestructure. Then, layer 47 of conductive material suitable for use inconnecting leads to the structure is selectively deposited onto exchangemagnet layer 48. To complete this embodiment, second dielectric layer 18is deposited onto layers 47 and 51 followed by the overall deposition ofupper primary magnetic shield 16.

Fifth Embodiment

The process of this embodiment is also for manufacturing a top spinvalve structure but, unlike the previous four embodiments, it makes useof two thin film shields. While adding slightly to the overallthickness, the two shield structure has the advantage that, since PW₅₀is defined by the distance between these two shields, even narrowerpulse widths can be obtained. Note also that this scheme is not limitedto conventional spin-valve structures. It is also readily applicable tosynthetic anti-ferromagnet SVs and Dual-SV applications.

Referring now to FIG. 6, this embodiment begins with the provision ofthe first (lower) of the two primary magnetic shields 15 on whichdielectric layer 17 is deposited. Now follows a key feature of theinvention, namely the deposition of thin film shield 66. The thin filmshield is a layer of high permeability (greater than 500) ferromagneticmaterial. It needs to have as high an electrical resistivity as possiblewithin other constraints of the structure. It is required to be at least5 times more resistive than the free layer. Since the latter is about 25micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to bepreferred. The thickness of the thin film shield should be such that themoment-thickness product (of the thin film shield) is 2-5 times that ofthe free layer. The presence of this thin film shield allows relativelythicker dielectric layers to be used, thereby reducing or eliminatingthe chances of shorting, while still being able to obtain very narrowfeedback pulse widths (namely PW₅₀).

With the thin film shield in place, decoupling layer 25 is laid downfollowed by the deposition of free layer 21. This is followed by thedeposition of non-magnetic layer 22 onto which is deposited pinned layer23. Next, onto pinned layer 23 there is deposited anti-ferromagneticlayer 24 for use as a pinning layer.

Now follows another key feature of the invention. On anti-ferromagneticlayer 24, decoupling layer 25 is deposited, followed by the depositionof a second thin film shield 67. The second thin film shield has thesame properties as the first thin film shield. The presence of the thinfilm shields allows a relatively large shield-to-shield spacing to bemaintained (thereby reducing or eliminating the chances of shorting)while still being able to obtain very narrow feedback pulse widths.

To initiate completion of the structure, trench 29 is formed usingconventional patterning and etching. This trench extends through thinfilm shield 67 down as far as the top surface of dielectric layer 17.The trench has a sidewall 30 that slopes at an angle of about 20degrees. Onto this sidewall, as well as the exposed surface ofdielectric layer 17, is selectively deposited layer 27 of aferromagnetic material (such as CoCrPt) that is suitable for use as apermanent magnet, the direction of permanent magnetization being set bya field that is present during deposition of the layer or by laterannealing in such a field. Layer 27 will serve to provide longitudinalbias to the structure, as discussed earlier.

With layer 27 in place, a layer of conductive material 28, suitable foruse as a connecting lead to the structure, is selectively depositedthereon. This is followed by the deposition of second dielectric layer18 onto which is deposited upper primary magnetic shield 16.

In FIGS. 7 and 8 we present data that confirms the effectiveness of thepresent invention. FIG. 7 illustrates the reduction in PW₅₀ that thepresent invention brings about. Shown there are micro-magnetic simulatedplayback wave-forms. The cases involved are curve 71, conventional SVhead with 800 Å shield-to-shield spacing (dashed), and curve 72 which isfor double-sided thin film shields(solid), the free layer being locatedat the center of the two thin film shields. The spacing between the thinfilm shields is 300 Å. The total distance between the primary shields isabout 1000 Å. The M_(r)T (remnant magnetization×layer thickness=totalmagnetic moment) of both thin film shields is four times that of thefree layer. The resistivity of the thin film shield is assumed to benine times greater than that of the free layer. Simulation shows thatthe PW₅₀ for the conventional SV is about 700 Å while the PW₅₀ for thethin film shield head is about 550 Å, which is approximately equivalentto a 450 Å shield-to-shield space in the case without the thin filmshields.

Since the thin film shields are magnetic materials, the fringe fieldfrom the shield layers will affect the performance of the free layer andcause instability if they are not properly biased. No additional biasscheme is needed for the continuous thin film shield. For the permanentmagnet (PM) abutted scheme (FIGS. 2, 3, and 6), a permanent magnet isplaced adjacent to both sides of the thin film shield to provide ahorizontal bias along the track width direction, just as the free layeris given its bias. The highly localized PM field removes the magneticcharge at the ends of the thin film shield, while still keep the highpermeability property of the shield layers.

From the curves shown in FIG. 7, the data displayed in TABLE II can bederived: TABLE II equivalent shield-to- structure PW₅₀ (Å) shieldspacing no TF shield 700 800 with TF shield 550 450

This shows that when the thin film shield disclosed in the presentinvention is used, the 550 Angstrom PW₅₀ that is obtained is equivalentto a shield-to-shield spacing of only 450 Angstroms.

FIG. 8 shows calculated transfer curves for the double-sided thin filmshield for two different PM bias strength presented as voltage vs. totalmagnetic moment in milli-electromagnetic units. A “kink” 83 appears inthe transfer curve where hard bias curve 81 for a field that is notstrong enough crosses curve 82 which is for a field of adequatestrength. Calculations show that a stability coefficient(M_(r)T)_(PM)/(M_(r)T)_(TFS) of 1 is sufficient to provide the properhorizontal bias for the thin film shields.

Note that since the thin film shield is at least two times thicker thanthe free layer, the degree of the magnetization rotation in the thinfilm shield is usually much less than in the free layer. Themagnetization in the thin film shield is essentially oriented along thetrack width direction. The change of the free layer bias level due tothe flux from the shield layer is not significant. The effect of currentfield from the thin film shield layers on the bias is also negligibledue to the high resistivity of the shield material.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1-2. (canceled)
 3. A process for manufacturing a top spin valvestructure, including a free layer, comprising: providing a lower primarymagnetic shield on which is a first dielectric layer; on the firstdielectric layer, depositing a layer of high permeability ferromagneticmaterial, said material having an electrical resistivity greater thanabout 125 micro-ohm-cm and a thickness such that the product of itsmoment and thickness is 2 to 5 times that of the free layer, therebyforming a thin film shield; on the thin film shield, depositing a layerof material suitable for use as a decoupling layer; on said decouplinglayer, depositing a layer of magnetic material suitable for use as thefree layer in said spin valve; on the free layer depositing a layer ofnon-magnetic material; on the layer of non-magnetic material, depositinga layer of magnetic material suitable for use as a pinned layer in saidspin valve; and on the pinned layer, depositing a layer of ananti-ferromagnetic material suitable for use as a pinning layer in saidspin valve, thereby completing formation of the top spin valve; thenpatterning and etching the structure to form therein a trench thatextends through the anti-ferromagnetic layer as far as said firstdielectric layer, said trench having a sidewall that slopes; on thefirst dielectric layer and on the sidewall, selectively depositing alayer of a ferromagnetic material suitable for use as a permanent magnetfor providing longitudinal bias to the structure; on the permanentmagnet layer selectively depositing a layer of conductive materialsuitable for use as a connecting lead to the structure; on theanti-ferromagnetic layer and on the conductive lead layer, depositing asecond dielectric layer; and on the second dielectric layer, depositingan upper primary magnetic shield.
 4. The process described in claim 3wherein the thin film shield is selected from the group consisting ofnickel-iron-chromium, cobalt-niobium-zirconium, cobalt-niobium-hafnium,iron-cobalt-nitrogen, iron-cobalt-chromium, iron-cobalt-tantalum, andiron-cobalt-titanium and has a permeability greater than about 500.5-20. (canceled)
 21. The process recited in claim 3 wherein saiddecoupling layer is selected from the group consisting of TaO, NiCr, andNiFeCr.
 22. The process recited in claim 3 wherein said decoupling layeris between 20 and 50 Angstroms thick.